Fixing the microwave oven
Some of the keys on my microwave stopped working recently. In the past this has been fixed with the timeless technique of forgetting about it and hoping for the best. This time the problem was more stubborn.
It's a fairly simple unit, so I pulled it apart looking for gremlins.
Here's what the keypad looks like from the front, and from the back.
The green flat flexible cable (FFC) on the left is the connection to the keypad. The keypad itself is a sealed unit, so I figured the problem was in the connection.
First I tried removing the FFC, blowing in the connector, wiping the connection pins and reseating the cable. With some pressing and probing, a few more keys started to work, until I happened upon the correct combination of presses and prods to get all the keys working. By the time I had it all back together however, less keys were working than before I took it apart.
From there I tried a bunch of stuff I was sure would fix it. I used various sprays on the electrical connections and cleaned the surfaces with sharp instruments. I even wedged a piece of plastic in to increase the pressure of the low-insertion force (LIF) connector, and trimmed the FFC so the connector gripped a fresh section. But the response of the keypad was getting worse.
Finally I bit the bullet and ran out to Jaycar to buy this $30 conductive pen.
My aim was to reapply the conductive pads that sit on the end of the FFC. Somehow the tiny pads allow electrical conductivity between the pins in the connector and the tracks within the FFC. It was surprisingly hard to be neat with the pen, but by carefully alternating between the pen and an X-Acto knife, I was able to create large, consistent pads on the end of the FFC.
This time, after the conductive ink had tried, as soon as I replaced the keypad in the microwave, all keys worked perfectly.
Long story short, a $30 conductive pen could save you a $200 microwave.